The invention relates to display panels, and in particular to display panels fabricated with low temperature poly-silicon process.
Thin film transistors (TFTs) in liquid crystal displays (LCDs) serve as pixel control elements. In general, TFTs can be divided into two categories, amorphous silicon TFT and poly-silicon TFT. The poly-silicon TFTs are typically applied in high-speed circuits and large LCDs due to high electron mobility, good IC density, and small leakage current thereof. In most LCDs, the poly-silicon TFTs are formed from low temperature poly-silicon (LTPS), so that size of the poly-silicon TFTs decreases and the aperture ratio increases.
FIG. 1 is a schematic diagram of a conventional display panel. A display panel 10 comprises a plurality of pixel cells 12 disposed in a matrix configuration. A polycrystalline semiconductor film is formed in advance on pixel cells 12 by a LTPS process. A laser then irradiates the polycrystalline semiconductor film corresponding to pixel cells 12 in each column to form the poly-silicon semiconductor film from polycrystalline semiconductor film. Eventually, a poly-silicon TFT 14 is formed in each pixel cell 12 by other processes.
Since the size of the laser beam is limited, the laser only irradiates the pixel cells in one column at a time and then irradiates the pixel cells in the next column by stepping. Accordingly, the characteristics of the pixel cells in the same column are the same. The intensity of each laser beam however is different, so that pixel cells irradiated by different laser beams yield the poly silicon TFTs with non-uniform characteristics. When the characteristics of the pixel cells in one column differ from that of the pixels in the other columns, the non-uniformity results in the display panel. This non-uniformity causes undesirable mura defects.